The performance and efficiency of spark ignition engines can be increased by increasing knock resistance. Direct injection of alcohol in spark ignition gasoline engines provides strong vaporization cooling of the fuel-air mixture in the cylinders and thereby substantially increases knock resistance. The increased knock resistance allows operation and higher compression ratio and/or higher levels of turbocharging.
The alcohol can be either directly injected from a single source by itself or along with gasoline or another fuel, or injected on-demand from a secondary tank into an engine that is primarily fueled with gasoline. For example, U.S. Pat. No. 7,225,787 and U.S. Pat. No. 7,314,033 describe gasoline engines in which on-demand use of ethanol or methanol from a secondary tank is employed to prevent knock at high torque.
Direct injection, however, has the disadvantage that if it is to be employed by modifying existing engines that are not direct injection spark ignition engines, it is necessary to change the engine head in order to provide the additional penetration for the direct injector. This can substantially increase the effort that is required for engine modification. An example is the conversion of a turbo diesel engine to a spark ignition engine that uses direct injection.
On-demand use of alcohol from port fuel injection can be employed as an alternative to direct injection and is described in U.S. Pat. No. 7,314,033. However, as discussed in this patent, it has the disadvantage that, while there is a knock resistance improvement from the higher chemical octane of the alcohol relative to gasoline, the vaporization cooling effect inside the cylinder is lost in conventional port fuel injection. In conventional port fuel injection, the air intake valve is closed when the fuel is injected in the manifold and the vaporization cooling takes place outside of the cylinder.
Use of open-valve port fuel injection of the alcohol bearing fuel can provide a way to maintain the advantage of ease of implementation of port fuel injection while also providing some vaporization cooling of the injected alcohol bearing fuel. In this case, some of the liquid fuel from the port fuel injector enters through the cylinder intake port and provides vaporization cooling of the fuel-air mixture.
Employment of two port fuel injectors, where the injectors inject different fuels and one of the injectors provides alcohol while the cylinder intake valve is open has been described in U.S. Pat. No. 7,647,916. However, it does not discuss a set of approaches that could be particularly effective in increasing the knock resistance of open-valve port fuel injection and minimizing the adverse effects of open valve port fuel injection. U.S. Pat. No. 7,647,916 also did not discuss other uses of open-valve port fuel injection to enhance the operating characteristics of spark ignition engines.
Therefore, improved means to maximize knock resistance and minimize the adverse effects of open-valve port fuel injection are needed. The use of open-valve port fuel injection to improve the capability of spark engines using direct injection and using different fuels would also be beneficial